Low bandgap polymers from fused dithiophene diester

ABSTRACT

The present invention involves monomeric compounds having the structure: ##STR1## Substituents W and Z are independently --CN, --NO 2 , -aryl, -aryl-V, --COX, SO 2  R, --H, or -alkyl. Substituent X is --OR, or --NR,R where R and R 1  are independently -alkyl or --H. Substituent V is -halide, --NO 2 , --CN, --SO 2  R, or --COX. At least one of W and Z is --NO 2 , --SO 2  R, --CN, --COX or -aryl-V. In one preferred embodiment substituents W and Z are both --CN. In another preferred embodiment, substituent X is --NO 2  or --CN and substituent Z is --C 6  H 4  NO 2 . These monomers are polymerized to form low bandgap polymers.

This is a nationalization of PCT/US92/07604 filed Sep. 9, 1992, that isa continuation-in-part of U.S. patent application No. 758,859 filed Sep.12, 1991, that issued as U.S. Pat. No. 5,274,058 dated Dec. 28, 1993.

BACKGROUND OF THE INVENTION

Since the discovery of high electrical conductivity in "doped"polyacetylene films in the mid-1970's, the field of electroactivepolymers has undergone explosive growth. The great interest in thesematerials stems from their potential use in electronic and opticalapplications. Electrical conductivity is typically achieved viaoxidative (or, more rarely, reductive) doping of the neutral polymers, apractice which is often accompanied by reduced processibility andenvironmental stability. Hence a major goal in this field is the designand synthesis of processible polymers with low or zero bandgaps.

The potential benefits from such low gap polymers are well recognizedand recent theoretical approaches have focused on bond lengthalternation (Bredas, et al., 1986; Toussaint, et al., 1989-2; Toussaint,et al., 1989-1; Bredas, J. L., 1985; Bakhashi, et al., 1987; Bredas, J.L., 1987; Kertesz, et al., 1987; Hanack, et al., 1991) and variations inoccupancy of frontier orbitals (Tanaka, et al., 1985; Tanaka, et al.,1987; Tanaka, et al., 1989; Tanaka, et al., 1988) to identify likely lowE_(gap) systems. Polyisothianaphthene (PITN) (Wudl et al., 1984), I, andits derivatives (Ikenone et al., 1984), with E_(gap) ≈1.1 eV representsome of the more successful experimental realizations of thesetheoretical predictions (Colaneri, et al., 1986; Kobayashi, et al.,1985). These polymers have E_(gap) 's 1 eV lower than theircorresponding parent, polythiophene, (PT) (Bredas, J. L., 1985). Thisreduction in E_(gap) is ascribed (Bredas et al., 1986) to an increasedcontribution of the quinoid structure, brought about by the 3,4-fusedbenzene ring. Thus, a considerable amount of the effort to date onnarrow band gap polymers has concentrated on increasing their quinoidcharacter. (See FIG. 1).

The energy difference between the aromatic and quinoid structure variesdepending on the neutral material's degree of aromaticity. For polymerslike polyphenylene, polythiophene, and polypyrrole, it can besubstantial so that very little of the quinoid resonance formcontributes to the neutral polymer's overall structure. Quinoid segmentscan be generated in these polymers by the doping process (Bredas, etal., 1984; Bredas, et al., 1982), however, and their growth followed byoptical spectroscopy (Chung, et al., 1984). The energy dissimilarity isreduced in PITN since the creation of the quinoid structure in thethiophene moiety is partially compensated by return of aromaticity tothe fused six membered ring. This observation has led to several otherapproaches for generating stable quinoid character. One (Toussaint, etal., 1989) is exemplified by structures like poly(2,7-pyrenylenevinylene), as shown in FIG. 2, structure IIa, to achieve the quinoidresonance form since in doing it exchanges one formally aromaticstructure for another (bold outline).

Hence polymer IIa is predicted to have a significantly lower bandgapthan the corresponding 1,6 isomer, IIb, (see FIG. 2) which does not havethis option (Toussaint, et al., 1989). A second approach does not relyon resonance stabilization to incorporate quinoid character but buildsit directly into the monomer and polymer (Toussaint, et al., 1989;Bredas, J. L., 1987; Kertesz, et al., 1987; Hanack, et al., 1991;Jenekhe, S. A., 1986, Wudl, et al., 1988; Zimmer, et al., 1984;Yamamoto, et al., 1981; Miyaura, et al., 1981; Kobmehl, G., 1983). Thesematerials are based on polyarene-methylidenes, III. Neutral films of III(X, Y=S, m=2, n=1) shown in FIG. 3 display absorption maxima around 900nm (Hanack, et al., 1991), reminiscent of other lowered E_(gap) polymerslike PITN.

Yet another approach to lowered E_(gap) materials exploits the bandcrossings between highest occupied (HO) and next highest occupied (NHO)orbitals or lowest unoccupied (LU) and next lowest unoccupied (NLU)orbitals. (Tanaka, et al., 1987; Tanaka, et al., 1988) that occur incertain polymers like polyphenylene and polyperylene.

Theoretically, derivatives with lowered E_(gap) 's can be obtained byadjusting the frontier orbital occupancy of the polymer. This would beaccomplished by replacing certain carbons with either electron rich(e.g., N) or electron poor (e.g., B) elements, their positions carefullychosen, while maintaining planarity. Systems predicted (Tanaka, et al.,1987; Tanaka, et al., 1988) to have lowered E_(gap) 's are structuresIV, V and VI shown in FIG. 4. The synthesis of such materials, however,could be arduous and their processibility is not expected to be high.

When adding heteroatoms, substituents and ring fusions, the symmetry ofthe frontier orbitals must be considered. Unlike polyacetylene whosebandgap depends primarily on the average bond length alternation (δr),this effect is a secondary contributor to the E_(gap) ofpolyheteroaromatics. This parameter is defined as the average of thedifference of neighboring long and short C--C bonds. E_(gap) is aminimum δr=0. (Lowe, et al., 1984; Grant, et al., 1979; Longuet-Higgins,et al., 1959; Kertesz, et al., 1981); Paldus, et al., 1983). Thedominant factor for heteroaromatics, however, is the strength of theinteraction between the carbon framework and the heteroatom and this isdependent on the symmetry of the former's frontier orbitals (Lee, etal., 1988; Mintmire, et al., 1987). When the highest occupied molecularorbital (HOMO) is antisymmetric and the lowest unoccupied molecularorbital (LUMO) symmetric (as is the case for aromatic arrangements), theband gap increases upon interaction with the heteroatom. The bandgap isdecreased, however, for the quinoidal bonding arrangement which has asymmetric HOMO and antisymmetric LUMO (see FIG. 5) (Lee, et al., 1988;Mintmire, et al., 1987). E_(gap) is minimized at some intermediatestructure. Thus polymers such as III, in which the frontier orbitals(HOMO and LUMO) are similarly perturbed by the heteroatom (thuscanceling its effect) are expected to have reduced E_(gap) 's (Lee, etal., 1988; Kertesz, et al., 1989; Lee, et al., 1990).

Polymer VII, formed by annulating a second ring onto PITM, has beenpredicted by some to be a material with a vanishingly small E_(gap).Subsequent calculations (Kertesz et al., 1989; Lee et al., 1990) andexperimental measurements (Wudl, et al., 1990) showed that VII (shown inFIG. 6) had a bandgap greater than PITN.

SUMMARY OF THE INVENTION

The present invention involves monomeric compounds having the structure:##STR2## Substituents W and Z are independently --CN, --NO₂, -aryl,-aryl-V, --COX, SO₂ R, --H, or -alkyl. Substituent X is --OR, or --NR,Rwhere R and R¹ are independently -alkyl or --H. Substituent V is-halide, --NO₂, --CN, --SO₂ R, or --COX. At least one of W and Z is--NO₂, --SO₂ R, --CN, --COX or -aryl-V. In one preferred embodimentsubstituents W and Z are both --CN. In another preferred embodiment,substituent W is --NO₂ or --CN and substituent Z is --C₆ H₄ NO₂.

In a preferred embodiment, substituent W is --CN and substituent Z is--COX, --SO₂ R, -alkyl, --H, aryl or -aryl-V. Substituent X is --OR or--NRR¹ where R and R¹ are independently --H or -alkyl. Substituent V is--NO₂, -halide, --CN or --SO₂ R.

In another embodiment, substituent W is --CF₃ and substituent Z is --SO₂R where R is --H or -alkyl.

In another preferred aspect, substituent W is --NO₂ and substituent Z isH or CO₂ R where R is --H or -alkyl.

A particularly preferred embodiment of the present invention involves acompound having the structure ##STR3## where substituent W is CN or NO₂and substituent Z is CO₂ R. Here, R is H or C_(m) H_(2m+1) and m is 1 toabout 16.

From a further view, the present invention concerns a compound havingthe structure ##STR4## Substituent V is --NO₂, -halide, --OR¹ or --NR¹R². Substituents R¹ and R² are independently --H or -alkyl.

Another novel compound of the present invention is one having thestructure: ##STR5## where R is H or alkyl. This compound, if aqueous oracidic conditions are avoided, may be polymerized into a low bandgappolymer.

In further view, the present invention includes novel low bandgappolymers. One such low bandgap polymer has the structure: ##STR6##Substituent X is O or NR and R is --H or -alkyl. The number of monomericunits (n) is typically 5 to about 500.

Preferred low bandgap polymers of the present invention have thestructure: ##STR7## Substituents W and Z are independently --CN, --NO₂,-aryl, -aryl-V, --COX, --SO₂ R, --H, or -alkyl. Substituent X is --OR or--NR,R¹, where R and R¹ are independently -alkyl or --H. Substituent Vis -halide, --NO₂, --CN, --SO₂ R, or --COX. At least one of substituentsW and Z is --NO₂, --SO₂ R, --CN, --COX or -aryl-V. The number ofmonomeric units (n) in the low bandgap polymer is preferably 5 to about500. In one preferred embodiment substituent W is --NO₂ and substituentZ is CO₂ R where R is --H or -alkyl. In another preferred embodiment,substituent W is CN or NO₂ and substituent Z is CO₂ R where R is H orC_(m) H_(2m+1) and m is 1 to about 16. Additionally, where substituent Wis CN or NO₂ and substituent Z is C₆ H₄ NO₂ an additional preferredpolymer is described.

In another preferred embodiment, where W=Z=COX where X is OR and R=C₂H₅, R=C₇ H₁₅ or R=C₁₆ H₃₃. Typical monomer syntheses are included on thefollowing pages.

Note the derivative with:

R=C₂ H₅ is Cyclopenta 2,1-b;3,4-b'!dithiophene-4-(bis carboxyethyl)methylidine (BCECPD)

R=C₇ H₁₅ is Cyclopenta 2,1-b;3,4-b'!dithiophene-4-(bis carboxyheptyl)methylidine (BCHCPD)

R=C₁₆ H₃ is Cyclopenta 2,1-b;3,4-b'!dithiophene-4-(bis carboxyhexadecyl)methylidine (BCHDCPD).

One preferred low bandgap polymer has the structure: ##STR8## wheresubstituent W is --CN and substituent Z is --COX, --SO₂ R, -alkyl, --H,aryl or -aryl-V. Substituent X is --OR or --NRR¹ where R and R¹ areindependently --H or -alkyl. Substituent V is --NO₂, -halide, --CN or--SO₂ R. The number of monomeric units (n) is again 5 to about 500.

In another embodiment of this low bandgap polymer, substituent W is--CF₃ and substituent Z is --SO₂ R where R is --H or -alkyl. The n isagain 5 to about 500.

Another low bandgap polymer of the present invention has the structure:##STR9## where X is --NO₂ --Cl, --OR¹ or --NR¹ R² where R¹ and R² areindependently H or alkyl. The n is again 5 to about 500.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the aromatic and quinoid character of polyisonapthalenepolymers (I).

FIG. 2 shows the aromatic and quinoid character of poly (2/7-pyrenylenevinylene), (IIa and IIb).

FIG. 3 shows structures of polyarene-methylidenes (III).

FIG. 4 shows structures predicted by others to have lowered E_(gap) 's(IV, V and VI).

FIG. 5 shows E_(gap) 's for polymers with carbon frameworks in aromaticand quinoid arrangements.

FIG. 6 shows the structure of a polymeric unit of PITN with a secondannulated ring (VII).

FIG. 7 shows the generalized fused bithiophene structure VIII.

FIG. 8 shows frontier orbitals of bithiophene, a substituted bithiophene(3,3'-dicyanobithiophene), and a fused bithiophene (CDM). The HOMO-LUMOseparations (and hence E_(gap) 's) follow the order Δ₁ >Δ₂ >Δ₃.

FIG. 9 shows a comparison of predicted and measured trends for (a) HOMOenergies with peak anodic potentials, and (b) HOMO-LUMO separation withE_(gap) 's.

FIG. 10 shows the structure of cyclopenta 1,2-b;3,4-b'! dithiophen-4-one(CDM) and its SYMBOLIC conversion to compounds of the present invention.

FIG. 11 shows synthetic schemes for certain monomers.

i: 1) NaBH₄, 2)H⁺ to produce VIIIa; ii: 1) RMgX, 2) TsCl, 3) LiAlH togive Z=R (XIIIa) or

ii: 1) NaBH₄, 2) base then RX to yield Z=OR (XIIIb);

iii: CH₂ (CN)₂, base (X); or W--CH₂ --Z, base where W≠Z=CN, COOR, CF₃,and the like!;

iv: RCH₂ NO₂, base on an imine derivative of IX

v: 1) ArLi, 2) H⁺, X=CH₃, Cl, H, OCH₃, or NR₂, for example.

FIG. 12 schematically shows the synthesis of fused bithiophene monomersbearing NO₂ and an R group.

FIG. 13 schematically shows the production of polymeric VIIIa (where Xis CH⁺) from polymeric XIII where Z is OH.

FIG. 14 shows a monomeric unit (XIV) for generating polymers withalternating monomer sequences (EWG=electron withdrawing group).

FIG. 14A shows a schematic representation of monomers of the presentinvention with α and β proton designations.

FIG. 14B shows relative NMR intensities of α and β protons related todegree of polymerization.

FIG. 15 schematically shows the monomeric structure ofpoly-4H-cyclopenta 1,2-b;3,4-b'!dithiophene-4-one (PCDT).

FIG. 16 shows the absorption spectrum for polythiophene (a) (solid line)and neutral poly-IX (b) (broken line).

FIG. 17 shows the difference absorption spectra (reference to V_(appl)=2.5 V vs. Li) as a function of doping for poly-IX. A:2.8V, B:3.4 V,C:3.5V, D:3.6V, E:3.8V, F:3.9V, G:4.0V.

FIG. 18 shows approximate energy level diagram for poly-IX. Levels wereestimated from spectral peak positions.

FIG. 19 schematically shows the monomeric structure ofpoly-4-dicyanomethylene-cyclopenta 2,1-b;3,4-b'!dithiophene-4 (PCDM) intwo resonance forms (XVa and XVb).

FIG. 20 shows the absorption spectrum for PCDM.

FIG. 21 shows a cyclic voltammogram of PCDM as a function of scan rate,showing p and n-doping. (a) 10 mV s⁻¹ ; (b) 20 mV s⁻¹ ; (c) 30 mV s⁻¹ ;(d) 40 mV s⁻¹ ; (e) 50 mV s⁻¹ ; (f) 60 mV s⁻¹ ; (g) 70 mV s⁻¹ ; (h) 80mV s⁻¹.

FIG. 22 shows the structure of carboxyethylcyanomethylene-4H-cyclopenta2,1-b;3,4-b'!dithiophene (C2CCPD).

FIG. 23 shows the structure of carboxycyanomethylene-4H-cyclopenta2,1-b;3,4-b'!dithiophene (CCPD).

FIG. 24 shows the structure ofcarboxyhexadecylcyanomethylene-4H-cyclopenta 2,1-b;3,4-b'!dithiophene(C16CCPD).

FIG. 25 shows the structure of carboxyhexylcyanomethylene-4H-cyclopenta2,1-b;3,4-b'!dithiophene (C7CCPD).

FIG. 26 shows the structure of p-nitrophenylcyanomethylene-4H-cyclopenta2,1-b;3,4-b'!dithiophene (NPCCPD).

FIG. 27 shows the structure of compounds of the present invention, whereW is NO₂, Z is COOR and R is H, alkyl or aryl.

FIG. 28 schematically shows the synthesis ofnitromethylene-4H-cyclopenta 2,1-b;3,4-b'!dithiophene (NMCPD).

FIG. 29 schematically shows the synthesis of Cyclopenta2,1-b;3,4-b'!dithiophene-4-(bis carboxyethyl) methylidine (BCECPD).

FIG. 30 schematically shows the synthesis of Cyclopenta2,1-b;3,4-b'!dithiophene-4-(bis carboxyheptyl) methylidine (BCHCPD).

FIG. 31 schematically shows the synthesis of Cyclopenta2,1-b;3,4-b'!dithiophene-4-(bis carboxyhexadecyl) methylidine (BCHDCPD).

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The monomer cyclopenta 1,2-b;3,4-b'!dithiophene-4-one (CDT) (see FIG.10) serves as a convenient starting point for other monomer systems.Reaction with active methylene compounds, WCH₂ Z where W and Z come froma large list of groups including: --CN, --NO₂, esters, amides,sulfoxides, sulfones, sulfonates, sulfonamides, aldehydes, ketones,haloalkyls, alkyls, and the like, is straightforward. Examples are givenbelow.

The systems described herein are unusual in several respects. First themonomers CDT and CDM have essentially the same peak anodic potentials(E_(pa) 's) as α-bithiophene (BT). This behavior is quite different fromother thiophene monomers substituted with electron withdrawing groupswhich have E_(pa) 's considerably higher (Waltman, et al., 1984) thanthe parent thiophene. Secondly, the E_(pa) 's of the correspondingpolymers, PCDT, PCDM and PBT are approximately equal. Despite thesesimilarities, the bandgaps are dramatically different. The obviousconclusion is that the energy of the HOMO level is not being stronglyaffected by substitution while the LUMO energy is being lowered. Thiscan be explained with the aid of FIG. 8 which displays the frontierorbitals for bithiophene, a substituted bithiophene(3,3'-dicyanobithiophene) and fused bithiophene, CDM. The respectiveHOMO-LUMO energy separations are Δ₁, Δ₂ and Δ₃.

Both the HOMO and LUMO of the substituted bithiophene are stabilizedcompared to bithiophene when electron withdrawing groups are placed atthe 3 and 3' positions. (See the left side of the FIG. 8). The LUMO isstabilized to a slightly greater degree, leading to a small reduction inHOMO-LUMO separation (Δ₂ <Δ₁). The situation is dramatically differentfor the fused system, however. (See right side of FIG. 8). Theantisymmetry of the HOMO in the fused system creates a node at the4-position making this orbital relatively insensitive to substitutionthere. This is the origin of the similar E_(pa) s of BT, CDT and CDM andthe analogous grouping of the E_(pa) s for their corresponding polymers.The symmetric LUMO for the fused system, however, is still stabilized bysubstitution with electron withdrawing groups (manifested by loweredhalf-wave reduction potentials). The E_(1/2) s for CDM, CDT and BT are-0.78 V, -1.17 V (Koster, et al., 1974) and <-2.00 V vs SCE (Jones etal. 1990), respectively. Since the reference HOMO level has not changedupon substitution, the net effect is a significantly reduced E_(gap) (Δ₃<<Δ₁). Since E_(gap) 's have been shown to parallel the Huckel HOMO-LUMOseparations (Kertesz, et al., 1989), this method can be used to rapidlyscreen monomers as to their potential of producing low E_(gap) systems.

To a first approximation, the HOMOs and the peak anodic potentials ofother fused bithiophene monomers should be approximately the same (theE_(pa) s of the corresponding polymers should also group at some lowervalue), regardless of the substituent. FIG. 9 gives the measured E_(pa)for several monomers/polymers of the present invention, along with thecalculated HOMO-LUMO differences and the associated bandgaps determinedfrom their optical absorption spectra. These several cases support thegenerality of the model.

FIG. 7 shows fused bithiophene structure VIII. The monomer/polymerfamilies labelled IX, X and XI (see FIG. 11) are thus far most clearlyunderstood. Compound VIII and family XII (see FIGS. 7 and 11) shouldalso display small bandgaps but are yet incompletely defined. Theacid-catalyzed dehydration step with VIII and XII to form thepolycations has yet to be fully defined.

Monomer Family X

One member of family X, namely CDM where W=Z=CN (XV, see also FIG. 19)as shown in FIG. 11 is discussed in detail elsewhere herein. Its polymerhas the lowest E_(gap) known to date and displays reversible p- andn-type doping. Other family members (e.g., W=CN; Z=COOX) are prepared bythe analogous Knoevenagel condensation chemistry of cyanoacetic acidderivatives with IX. Initial results are particularly good on thesystems where X=H, C₂ H₅, n-C₇ H₁₅ and n-C₁₆ H₃₃. Those skilled in theart understand that a variety of other alkyls will function likewise.These monomers all have E_(pa) s around 1.2 V (vs SCE) and theirpolymers display electronic absorption thresholds at <0.9 eV. The verymoderate increase in E_(gap) for these polymers compared to PCDM isconsistent with the somewhat lowered electron withdrawing ability of acarboxyl compared to a nitrile (for various approaches and parametersquantifying substituent effects see "Mechanism and Theory in OrganicChemistry," Lowry et al ). They are still below 1 eV, though, and thereis now a convenient functionality (i.e., the X group of the ester) withwhich to alter mechanical/solubility properties. Since different n-alkylsubstituents will not significantly affect the electronics of the ester,copolymers of various cyanoester derivatives can also be used tooptimize the physical properties. Similarly, X can be ethylene oxideoligomers or ω-alkylsulfonates. Each imparts enhanced (aqueous)solubility and the latter leads to "self-compensating" (Havinga, et al.,1989; Patil, et al., 1987; Reynolds, et al. 1988) polymers. Since theE_(gap) 's will be below 1 eV, lowered doping levels will be required toobtain electrical conductivity.

Based on the strong electron-withdrawing abilities of the nitrile andnitro groups, the condensation products between IX and nitroacetonitrile(W=CN, Z=NO₂) or dinitromethane (W=Z=NO₂) afford polymers with E_(gap)'s even lower than PCDM (E_(gap) ≦0.8 eV). The dinitromethylenederivative of fluorenone is a known compound and is made through theaction of iodonitroform with fluorene (Gabitov, et al., 1969).

The present invention involves a design strategy which appreciates thatthe quinoid structure arises at the expense of aromatic character bututilizes a different mode to reduce the latter. The monomers of thepresent invention are conceptually based on the antiaromatic (12πelectron) system, shown in FIG. 7, (VIIIa, X=CH⁺) which displays areduced HOMO-LUMO separation (Zhou, et al., 1989) compared to relatedaromatic (14π electron) fused systems (e.g., VIII; X=S (Jow, et al.,1986), O, or NH). Simple Huckel calculations give HOMO-LUMO differencesof 0.162, 1.113, 1.038 and 1.116β for the X=CH⁺, S, O and NH derivativesof VIII, respectively. This model is successfully used to produceseveral low band gap polymers.

The monomers disclosed here possess a structure capitalizing on theantisymmetry of their highest occupied molecular orbitals (HOMO's) so asto have the energy of these states essentially unaffected by theincorporation of substituents at certain positions. The symmetry of thelowest unoccupied molecular orbitals (LUMO's) does allow for substituenteffects on the energy of this orbital and is lowered when they areelectron-withdrawing. This results in a reduction of the HOMO-LUMOseparation and hence the bandgap (E_(gap)). This represents a newapproach to reduced E_(gap) polymers.

Polymers from these materials have likely use in electrochromics,electrode materials, semiconductor devices (diodes, thin filmtransistors, solar energy conversion, etc.). Electrochromic uses, forexample, include: windows which darken or lighten upon application of apotential in autos, homes, commercial buildings; large scale flatdisplays.

The present invention also involves a new method for producing lowbandgap (E_(gap)) polymers. The central feature involves using fusedmonomers with highest occupied (π) molecular orbitals (HOMOs) that arerelatively insensitive to substitution and lowest unoccupied orbitals(LUMOs) whose energies depend strongly on these substituents. Thepolymer "bandgaps" parallel the HOMO-LUMO separations. The polymers ofthe present invention have the lowest E_(gap) 's reported to date andseveral new families are presented whose E_(gap) 's should be lowerstill. Strategies for increasing processibility while maintaining lowE_(gap) 's are also provided. The environmental and mechanicaldifficulties that often plague doped polymers should be alleviated forour lowered bandgap materials. The apparent generality of certain fusedthiophenes suggests several families of low bandgap materials. These aresummarized in FIG. 11. Investigations have been conducted onrepresentative members in a number of these. Compound IX is clearly animportant starting material for these systems and can be obtained from arelatively straightforward literature procedure (Jordens, et al., 1970).In the following sections those systems on which the most proofs havebeen achieved are described.

FIG. 11 shows synthetic approaches to proposed monomers, i.1) NaBH₄,i.2)H⁺ ; ii.1) RMgX, ii.2) TsCl, ii.3) LAH to give Z=R (XIIIa) or ii.1)NaBH₄, ii.2) base then RX to yield Z=OR (XIIIb); iii) CH₂ (CN)₂, base(X); or W--CH₂ --Z, base where W≠Z=CN, COOR, CF3, etc!; iv) RCH₂ NO₂,base on imine derivative of IX (Charles, G., 1960) (the analogousreaction with the imine of fluorenone is known (Charles, G., 1963); v.1)ArLi, v.2) H⁺, X=CH₃, Cl, H, OCH₃, NR₂, etc.

The large number of active methylene compounds that can undergoKnoevenagel-type reactions with IX allows extraordinary latitude intailoring the properties of the resulting materials. Derivatives fromreadily available cyanoacetamides (W=CN, Z=CONH₂, CONHR, CONR₁ R₂),ring-substituted phenylacetonitriles (W=CN, Z=--C₆ H₄ --X, X=--NO₂,halogens, --NR₂, --NR₃ ⁺, --OR, -alkyl, for example), sulfones (e.g.,W=--CF₃, Z=--SO₂ R), nitroacetates (e.g., W=--NO₂, Z=--COOR) are but afew possibilities.

Active methylene compounds that can undergo condensations with carbonylcompounds may be used. Obviously, some would be better than others(especially the ones bearing strong electron withdrawing groups thatremain in conjugation with the fused bithiophene system).

Monomer Family XI

The single nitro group in monomers based on XI is sufficient to lowerthe bandgap in their corresponding polymers to at least the level ofPCDM. The processibility of this family of polymers is enhanced overPCDM, due to the incorporation of alkyl substituents (R). These monomersare prepared according to Scheme I, shown in FIG. 12. This is the Henryreaction, an analogous condensation between nitroalkanes and fluorenoneimine having been reported (Charles, 1963). This synthetic chemistry isused for preparing the derivative from nitroethane (R=CH₃). The higherhomologs, e.g. R=C₇ H₁₅ through C₁₆ H₃₃ are also so prepared. This rangeof alkyl group length produces the best properties thus far noted forpoly 3-alkylthiophenes with respect to processibility, effective degreeof conjugation and ultimate conductivity (Roncali, et al., 1987).

Monomer Family XIII

One of the important criteria for good electrical conductivity inpolymers is the ability of adjacent rings to assume substantiallycoplanar arrangements. Although the fused systems outlined in FIG. 11have the advantage of forced coplanar arrangement of the thiopheneswithin the individual monomeric units, this does not guarantee thatcoplanarity can always be achieved between repeat units. It is knownfrom studies on other substituted heteroaromatics that the introductionof substituents which increase the processibility of these polymers cansometimes present steric constraints to this coplanarity requirement(Ferraris, et al., 1989; Cannon, D. K. (1990); Ferraris, et al., 1990).Molecular mechanics calculations on several of the above mentionedoligomers show that the substituents are sufficiently far removed fromthe adjoining repeat unit so as not to interfere with the achievement ofsubstantially coplanar arrangements. This is also the case for monomerfamily XIII. Even though the electronic factors are not expected to leadto materials with E_(gap) 's as low as families X and XI, polymers fromfamily XIII benefit from the forced coplanarity in the repeat unit andpossess significant processibility. The relatively straightforwardchemistry leading to monomer family XIII facilitates a rapidoptimization of the electrical-mechanical property balance.

Monomer VIIIa and Family XII

Monomer VIIIa shown in FIG. 7 where X is CH⁺ is the simplest of thesesystems, but cannot be used to generate the corresponding polymerdirectly. Rather, the alcohol (XIII, Z=OH shown in FIG. 11) readilyproduced via reduction of CDT, can be polymerized into coherent films.Spectral measurements on acid-promoted doping of this polymer indicatethat the amount of doping is controlled by the amount of acid which isintroduced. Even though poly-VIII is a charged species, somestabilization is seen from the two flanking aryl rings (e.g., see FIG.13).

Even higher stabilities of the polycation should be manifested by thepoly-XII family since here the carbocation is flanked by three aromaticrings, at least two of which are held coplanar to the cationic orbital.Furthermore, substituents on the phenyl ring supply different amounts ofelectron density to this site, thus offering another method to controlthe electronics. The poly-XII family is generated from the correspondingalcohols and then subsequently dehydrated.

Copolymers

Since most of the monomers possess very similar E_(pa) 's,electrochemical copolymerization of them is feasible. This allows thebest physical properties of processible polymers to be blended with lowE_(gap) polymers. Although the overall composition and/or sequencedistribution of particular polymers will depend on the detailed kineticsof the propagation steps, such copolymerizations are less complicatedthan those between monomers of widely different oxidation potentials.Copolymers with alternating monomer sequences are generated frommonomers like XIV (see FIG. 14). When the groups flanking the fusedbithiophene moiety are comparatively electron rich, intramolecular redoxleads to materials with even lower bandgaps (Kowalik, et al., 1991).

Described herein is a general method for obtaining families of lowbandgap polymers and directions for development of this new class ofmaterials. The polymers are characterized with respect to theirelectrical, electrochemical, optical properties and, where appropriate,mechanical properties. The environmental and mechanical problems thatare often associated with doped polymers are greatly reduced in thesesystems.

The monomers of the present invention are readily polymerized, forexample, to form polymers having from 5 to about 500 monomeric units.Such polymerization involves an initial dissolution of the monomers in asolvent which is stable to oxidative conditions, for example chloroformor nitrobenzene. Polymerization is typically initiated byelectrochemical anodic effects or by chemical oxidants. Typical chemicaloxidants which may be used include ferric chloride, ferric perchlorate,cupric perchlorate, and nitrosyl salts such as nitrosoniumtetrafluoroborate (NOBF₄) and nitrosonium hexafluorophosphate (NOPF₆).Those skilled in the art may identify further oxidants likely to beusable. The polymerizations are carried out at ambient temperatures butelevated temperatures may also be used, if desired.

The polymerization of the monomers of the present invention is effectedthrough either electrochemical or chemical oxidation as describedherein. These polymerization methods are fairly standard methods toanyone working in the field and have been reported in the literature.

Polymerizations using FeCl₃ as a (chemical) oxidant are, for example,shown in Sugimoto et al. and Leclerc et al.

A typical procedure for this oxidative polymerization is:

A 50 mL 3 neck flask equipped with a magnetic stirring bar is chargedwith 0.65 gm (4 mmol) anhydrous FeCl₃ and 40 mL of anhydrous CHCl₃. Tothe stirred mixture 0.75-1.0 mmol of the appropriate monomer in 10 mLanhydrous CHCl₃ is added dropwise. An immediate color change of themixture is observed. Upon completion of the addition, the mixture isstirred at room temperature for 24 hours after which the solvent isremoved, for example, under vacuum. The residue is extracted withmethanol then acetone (e.g., by a Soxhlet extractor, each for about 24hours).

A typical procedure for electrochemical polymerization follows: Anassembly of a planar working electrode (e.g., indium-tin oxide coatedglass) and counter electrode (e.g., Al) held parallel to each other areplaced in a 10 mM solutino of monomer in acetonitrile containingsupporting electrolyte (e.g., 0.25 M LiBF₄). A constant current (e.g.,at current density of 300 μA/cm²) is applied for several minutes todeposit the polymer. The assembly is removed and rinsed with freshacetonitrile to remove unreacted monomer, soluble oligomers andelectrolyte. Polar aprotic solvents stable to the electrooxidativeconditions (for example propylene carbonate, nitrobenzene, acetonitrile,etc.) can be used. Supporting electrolytes like tetraalkylammonium oralkali. metal fluoroborates, hexafluorophosphates, perchlorates, etc.,can be used. Other working electrode materials like stainless steel,carbon, etc., can also be used.

Other electrode/solvent/electrolyte combinations are usable and arereported in the literature.

In the case of cyclopenta 2,1-b;3,4-b'!dithiophene-4-(biscarboxyhexadecyl) methylidine (BCHDCPD), the polymers grown byelectrochemical and chemical oxidations were soluble in common organicsolvents such as methylene chloride, chloroform, nitrobenzene andtetrahydrofuran (THF). This allowed ready further characterization bysize exclusion chromatography (SEC) and ¹ H NMR. The former wasconducted using a Varian VISTA series HPLC equipped with SEC columnsfrom Phenomenex (50 A and 1000 A), THF eluant (1 mL/min), UV (254 nm) orR1 detection. Polystyrene standards (Toyo Soda Mfg.) of molecularweights 1.3×10⁶, 1.72×10⁴, 2.8×10³ and 5×10² were used as calibrationstandards. ¹ H NMR spectra were collected at 270 MHz using CHCl₃solutions of Cyclopenta 2,1-b;3,4-b'!dithiophene-4-(biscarboxyhexadecyl) methylidine (BCHDCPD) and were referenced totetramethylsilane internal standard. The degree of polymerization (n)could be estimated from these techniques. The n's estimated by SECwere >5-10. There is some ambiguity in SEC molecular weightdeterminations in which the instrument has been calibrated usingstandards (here polystyrene) which may not have the same hydrodynamicproperties as the polymers being tested see Holdcroft!. The NMRmeasurements are essentially an end-group analysis. Here the absorptionsin the aromatic region for the polymer and monomer are compared. Twosets of peaks appear for the monomer in this region--one for theα-protons and one for the β=protons (see structure of FIG. 14A). Uponpolymerization, these two collapse into one absorbance. By comparing theintensity of this new peak to the minimum detectable intensity (i.e.,the baseline signal-to-noise intensity) n may be estimated forpolycyclopenta 2,1-b;3,4-b'!dithiophene-4-(bis carboxyhexadecyl)methylidine (BCHDCPD) by NMR. Such estimates gave n>40-50. As may beseen from FIG. 14B, this type of end-group analysis becomes lessaccurate as n increases (note small slope change between degree ofpolymerization 40 and 100) so values for n represent a lower limit.

The following examples describe preferred embodiments and best modes ofthe present invention and should not limit the scope of the presentclaimed invention.

EXAMPLE 1 Narrow Band Gap Polymers: Polycyclopenta1,2-b;3,4-b'!dithiophen-4-one

An electroactive polymer with a lowered band gap is obtained from themonomer cyclopenta 2,1-b;3,4-b'!dithiophen-4-one, alternatively -Poly(4-oxo-4H-cyclopenta 2,1-b;3,4-b'!dithiophen-2,6-diyl).

Much of the effort to date on narrow band gap heteroaromatic polymersfocuses on increasing their quinoid character. The present designstrategy recognizes that quinoid character arises at the expense ofaromatic character and that other modes of reducing aromaticity are alsoeffective in reducing E_(gap). This approach is used to identify afamily of monomers that yield lowered band gap materials compared to PT.Certain monomers of the present invention are based on the non-aromatic(12π electrons) 4H-cyclopenta 2,1-b;3,4-b'!dithiophen-4-yl cation VII(X=CH⁺) model which is expected to display a reduced HOMO-LUMOseparation (Zhou et al., 1989) compared to related aromatic fusedsystems. Furthermore, incorporation of the empty p orbital at the4-position affects the occupancy of the frontier orbitals similar tosubstitution by boron at that position which Tanaka et al. (Tanaka etal., 1985; Tanaka et al., 1987) have theoretically shown could reducethe band gap in other cases.

Since environmental stability of the cationic VIIa might be limited,(Koster et al., 1976) cyclopenta 2.1-b;3,4-b'!dithiophen-4-one IXa (FIG.15) was chosen (Jordens et al., 1970) as a first approximation to it.Contribution from IXa's primary resonance form, IXb was expected toreduce the aromaticity of the system. The results of electrochemical andspectral studies on poly-IX are reported (Lambert et al., 1991).

Cyclic voltammetry: Repetitive cyclic voltammograms (RCV) of IX areobtained by multiple scans of a 0.01 mol dm⁻³ solution of IX innitrobenzene-tetrabutylammonium tetrafluoroborate (0.1 mol dm⁻³)(TBATFB) between -0.63 and +1.47 (vs. SCE) at 100 mVs⁻¹. Cyclicvoltammetry (CV) of poly-IX is accomplished by galvanostatically growingthe polymer on the end of a 100 μm diameter platinum electrode,transferring the electrode to fresh electrolyte nitrobenzene-TBATFB (0.1mol dm⁻³)!, and scanning between 0.00 to +1.20 V (vs. SCE) at ratesranging from 5 to 100 mVs⁻¹. The peak anodic potential (E_(pa)) of thepolymer is determined by extrapolation to zero scan rate. (SCE=Standardcalomel electrode).

Spectroelectrochemistry: Thin films of poly-IX are depositedgalvanostatically from 0.01 mol dm⁻³ solutions of monomer innitrobenzene-TBATFB (0.1 mol dm⁻³) onto indium/tin oxide (ITO) coatedglass electrodes. Their spectroelectrochemistry is examined in 0.1 moldm⁻³ LiBF₄ -propylene carbonate (PC) by holding the film at a series ofconstant potentials and recording the spectra from 340 to 2100 nm.

The repetitive cyclic voltammetry (RCV) of IX is typical of a conductingpolymer growing on the electrode with each scan. After several scansboth monomer and polymer oxidation is observed, with the latteroccurring at a lower potential. The E_(pa) of IX is +1.26 V (vs. SCE)compared to +1.20 V (vs. SCE) for α,α'-bithiophene measured underidentical conditions. Thus, to a first approximation, the carbonylmoiety does not appear to alter greatly the position of the HOMO in IXcompared to α,α'-bithiophene. This is consistent with the antisymmetryof that orbital which places a node at the carbonyl., The E_(pa) ofpoly-IX is +0.75 V (vs SCE) compared to +0.70 V (vs SCE) for poly(α,α'-bithiophene). (Skotheim, 1986) The peak anodic current is a linearfunction of scan rate, as expected for a substrate affixed to theelectrode.

Ketone IX displays its lowest π,π transition at γ_(max) =472 nm (Kosteret al., 1979) (ε=1250). The π,π* nature of this transition is supportedby solvent effects and PPP (Koster, 1979). Upon electropolymerization,this long wavelength absorption shifts to 740 nm in the neutral polymerFIG. 16(b)!, a red shift of ≧200 nm compared to PT FIG. 16(a)!. (Chunget al. 1984) A strong absorption at 425 nm is also present in poly-IX.The difference absorption spectra of this polymer as a function ofapplied potential (referenced to the neutral polymer, V_(appl) =2.5V)are displayed in FIG. 17. The evolution of these spectra can beinterpreted within the bipolaron formalism (Chung et al.., 1984) if itis assumed that the lower energy absorption in neutral poly-IX isderived primarily from the aromatic HOMO-LUMO transition and the higherenergy transition arises between some deeper level (ALOMO) and the LUMO.One then obtains the characteristic growth of the aromatic HOMO (AHOMO)to quinoid LUMO (QLUMO) and AHOMO to quinoid HOMO (QHOMO) bipolarontransitions (1.1-1.2 eV and ≦0.7 eV, respectively) as the polymer isp-doped to higher levels. Ordinarily this would be accompanied by acomparable decrease in the AHOMO-ALUMO absorption intensity. Theobserved apparent modest decrease in this absorption upon doping and thetwo isosbestic points at 2.5 and 2.3 eV can be rationalized with theapproximate energy level diagram in FIG. 18. As the polymer is p-doped,the AHOMO→QHOMO, AHOMO→QLUMO, ALOMO→QHOMO and ALOMO→QLUMO transitionsgrow while AHOMO→ALUMO and ALOMO→ALUMO transitions decrease. Thedecrease in the AHOMO→ALUMO appears small because it is offset byincreases in the ALOMO→QLUMO and ALOMO→QHOMO occurring overapproximately the same wavelength range. The isosbestic points at 2.3and 2.5 eV result from the overlap of the ALOMO→QLUMO and ALOMO→QHOMOtransitions with the AHOMO→ALUMO transition. Similar arguments would beinvolved if the 424 nm transition were between the AHOMO and higherunoccupied aromatic and quinoid levels. The E_(gap) of the neutralpolymer, determined from the point of zero crossing of lightly dopedpolymer (Chung et al., 1984) (<3.4 vs. Li/Li⁺) is ≦1.2 eV. This gap is≧0.8 eV lower than that for PT (Chung et al., 1984) and only 0.2 eVhigher than that of PITN. (Wudl et al., 1984).

This model, which proposes the incorporation of non-aromatic characteras a route to reduce band gap polymers, succeeds for this polymer and itis noted that experiments on polymers derived from the Knoevenagelcondensation product of IX with malononitrile and cyanoacetic estersalso support this model. (See following Examples) Poly-IX joins a selectgroup of conducting heteroaromatic polymers with E_(gap) <1.5 eV.

EXAMPLE 2 Narrow Bandgap Polymers: Poly-4H-cyclopenta2,1-b;3,4-b'!dithiophene-4-dicyanomethylidene (PCDM)

An electroactive polymer with a bandgap of ≈0.8 eV is obtained from themonomer 4-dicyanomethylene-4H-cyclopenta 2,1-b;3,4-b'!dithiophene, (CDM)(See FIG. 19).

The dicyanomethylene group in CDM (XV) shown in FIG. 19, is a strongerelectron withdrawing substituent than the carbonyl in IX and shouldenhance the participation of XV's primary resonance contributor, XVb, tothe overall structure of the molecule. This in turn is expected toreduce the HOMO-LUMO separation in the monomer, and the E_(gap) in itspolymer, PCDM.

The UV/Vis spectrum of CDM displays a 100 nm (0.48 eV) red shift of thelong wavelength absorption band compared to CDT (γ^(IX) _(max) =472 nm,ε^(IX) =1250; γ^(XV) _(max) =576 nm, ε^(XV) 1450). This band wasassigned as a π- π* absorption for IX. The analogous absorption in XV isassigned to a π- π* transition based on the presence of structure inthis band, its 20 nm red shift from hexane to methanol, and by analogyto IX. Upon polymerization this band shifts to 950 nm in neutral PCDM, ared shift of ≈0.9 eV compared to the monomer and similar in magnitudeand direction to that observed upon polymerization of CDT.

The UV/Vis/NIR spectrum of neutral PCDM (see FIG. 20) shows the longwavelength band edge (E_(gap)) at ≈0.8 eV, making it one of the lowestbandgap polymers reported to date. PCDM is grown galvanostatically ontoindium tin oxide (ITO) coated glass electrodes at 750 mA/cm² for 3 min.from 0.01 M solutions of CDM in nitrobenzene containing 0.1 Mtetrabutylammonium tetrafluoroborate (TBATFB), and thenelectrochemically reduced at +2.8 V vs Li/Li⁺.! Cyclic voltammetry (CV)of PCDM yields a peak anodic potential (E_(pa)) of +0.76 V vs SCE PCDMwas grown on a 100 μm dia Pt disk electrodes from 0.1 M solutions of CDMin nitrobenzene containing 0.1 M TBATFB and then rinsed withnitrobenzene. The E_(pa) is determined by extrapolating to zero scanspeed a series of CV's taken between 0.0 and +1.2 V vs. SCE.! Forcomparison, PCDT and polybithiophene (PBT) display E_(pa) 's at +0.75(Lambert et al. 1991) and +0.70 (Skotheim, 1986) V vs SCE, respectively.Anodic and cathodic CV (The potential was scanned from +0.16 to +1.16 to-0.89 to +0.16 V vs SCE) of PCDM (see FIG. 21) shows both oxidation andreduction of the polymer. (The source of the oxidation wave peaking ≈0.5V vs SCE following each cathodic scan is not identified but it appearsonly if a cathodic scan precedes an anodic scan. This oxidation waveshows no discernible reduction. It appears associated with the absorbedpolymer rather than an impurity in solution since its current islinearly related to scan rate.) The difference in the thresholdpotentials for hole (p-doping) and electron (n-doping) injection is ≈0.3V, comparable to that of PITN (Kobayashi et al., 1985; Kobayashi et al.,1987), and indicative of a narrow E_(gap) material (Kaufman et al.,1983). However, whereas PITN is unstable to n-doping (Amer et al.,1989), PCDM appears stable to both p and n-doping after repeated anodicand cathodic cycling. FIG. 21 shows a cyclic voltammogram of PCDM as afunction of scan rate, showing p and n-doping. (a) 10 mV s⁻¹ ; (b) 20 mVs⁻¹ ; (c) 30 mV s⁻¹ ; (d) 40 mV s⁻¹ ; (e) 50 mV s⁻¹ ; (f) 60 mV s⁻¹ ;(g) 70 mV s⁻¹ ; (h) 80 mV s⁻¹.

Dicyanomethylene-4H-cyclopenta 2,1-b;3,4-b'!dithiophene (CDM)

In the above embodiment, malononitrile (0.26 mmole) in 10 mL of 95%ethanol is added to 50 mg (0.26 mmole) CDT in 25 mL of 95% ethanol whichcontained 2 drops of piperidine. The reaction mixture is stirred at roomtemperature of 10 min., the residue filtered and washed with water.Recrystallization one time from acetonitrile gives analytically pure CDM(e.g. 56 mg, 93% yield), m.p. 257-258 C. Elemental Analysis: FoundCalculated! for C₁₂ H₄ N₂ S₂ : % C, 59.58 59.98!; % H, 1.82 1.68!; % N,11.27 11.66!. uv/vis: γ_(max) (ε):576 nm (1450).

EXAMPLE 3 Cyanoester and amide derivatives

Cyanoester and amide derivatives are also prepared by analogousKnoevenagel-type condensation reactions involving cyanoacetic acidesters or amides (NCCH₂ COX; X=OR where R is derived from an alkyl oraryl alcohol or X is NRR' where R and R' are various combinations of H,alkyl and aryl substituents). Typical procedures for several of theseare as follows.

EXAMPLE 4 Carboxyethyl,cyanomethylene-4H-cyolopenta1,2-b;3,4-b'!dithiophene (C2CCPD)

In another embodiment, ethylcyanoacetate (0.26 mmole) in 10 ml absoluteethanol is added to 50 mg (0.26 mmole) of CDT in absolute ethanol. e.g.,25 ml containing potassium hydroxide, e.g., 10 mg. A reflux condenser isfitted to a drying tube and the mixture refluxed for 12 hours, pouredinto 25 ml water and then extracted, e.g., 3X with dichloromethane e.g.,20 ml. The organic layer is washed with 20 ml of aqueous NaHCO₃, dried,e.g., over anhydrous MgSO₄, filtered and the solvent removed in vacuo.The residue is recrystallized from 20 ml acetonitrile to affordanalytically pure C2CCPD, see FIG. 22 (e.g., 45 mg, 60% yield), mp164-65 C. Elemental Analysis: Found Calculated!for C₁₄ H₉ N₁ O₂ S₂ : %C, 58.18 58.52!; % H, 3.35 3.16!; % N, 4.63 4.87!.

EXAMPLE 5 Carboxycyanomethylene-4H-cyclopenta 2,1-b;3,4-b'!dithiophene(CCPD)

CCPD (see FIG. 23) is prepared in 71% yield in a procedure analogous tothat for C2CCPD except for the substitution of cyanoacetic acid forethylcyanoacetate.

EXAMPLE 6 Carboxyhexadecyl,cyanomethylene-4H-cyclopenta2,1-b;3,4-b'!dithiophene (C16CCPD)

Hexadecylcyanoacetate (e.g., 170 mg, 0.55 mmole), 100 mg (e.g. 52 mmole)of CDT and e.g. 50 μM piperidine in benzene e.g., 5 ml are refluxedtogether e.g., overnight. The reaction mixture is chromatographed oversilica gel with hexane elution. The C16CCPD (purple fraction) iscollected (e.g. 108.8 mg, 44% yield, mp 73 C). (See FIG. 24).

EXAMPLE 7 Carboxyhexyl,cyanomethylene-4H-cyclopenta2,1-b;3,4-b'!dithiophene (C7CCPD) (FIG. 25)

Heptyl cyanoacetate (123.7 mg, 0.67 mmole), CDT (100 mg) and 50 μlpiperidine are placed in 10 ml benzene and refluxed overnight.Chromatography over silica gel with hexane elution affords C7CCPD (e.g.90.3 mg (48% yield)), m.p. 57 C.

EXAMPLE 8

Other active methylene derivatives (WCH₂ Z) may also be condensed withCDT with base catalysis. For example, ring-substituted arylacetonitriles(W=CN, Z=--C₅ H₄ --X, X=H₁ --NO₂, halogens, NR₂, --NR₃ ⁺, --OR, alkyl,aryl, and the like) are prepared by the following procedure.

p-Nitrophenyl, cyanomethylene-4H-cycolopenta 2,1-b;3,4-b'!dithiophene(NPCCPD)

p-Nitrophenylacetonitrile (86 mg, 53 mmole), 100 mg CDT and 100 μlpiperidine are placed in 3 mL of benzene and refluxed overnight. Thereaction mixture is extracted with ether, subsequently washed with 10%acetic acid, aqueous NaHCO₃ then water, dried and the solvent removed invacuo to afford 105 mg NPCCPD (e.g., 86% yield) mp 223-5 C. See FIG. 26.

Derivatives where W=NO₂ and Z=COOR (R=H, alkyl, aryl) are also readilyprepared from nitroacetates (themselves easily obtained fromesterification of the dianion of nitroacetic acid obtained from thereaction of nitromethane with KOH). See FIG. 27.

EXAMPLE 9 Nitromethylene-4h-cyclopenta 2,1-b;3,4-b'!dithiophene (NMCPD)

Nitroalkyl (or aryl) derivatives (W-- --NO₂, Z=H, alkyl, aryl) areprepared by the Henry reaction on the imine of CDT.

CDT (e.g. 50 mg) is dissolved in methanol, e.g., 15 mL the solutionsaturated with anhydrous ammonia gas and the reaction vessel sealed. Themixture is allowed to stand at room temperature for one to two weeksafter which it is neutralized (with, e.g., concentrate H₂ SO₄) and theblue precipitate filtered. The collected solid is redissolved inconcentrated aqueous ammonia and extracted with ether. The solution isdried over MgSO₄ and the solvent removed in vacuo. The remaining solidis dissolved in nitromethane, refluxed (e.g. overnight) and the reactionmixture evaporated to dryness. The product, NMCPD, is purified forexample, by column chromatography over silica gel with CHCl₃ elution;m.p. 162-4 C. See FIG. 28.

Substitution of other nitroalkanes for nitromethane affords derivativesin which the --H has been replaced by alkanes or aryls.

EXAMPLE 10 Cyclopenta 2,1-b;2,4-b'!dithiophen-4-(bis carboxyethyl)methylidene (BCECPD)

In a 50 ml round bottom flask, 5 ml of dry THF were chilled to 0° C.under a nitrogen atmosphere. Then a solution of 0.25 Ml TiCl₄ in 0.5 MlCCl₄ was added dropwise with vigorous stirring. A bright yellowprecipitate was formed, and then a solution of 50 mg (0.26 mmol) ofketone (IX) and 40 Ml (0.26 mol) of diethyl malonate in 5 Ml THF wereadded. When mixing was completed, a solution of 450 Ml pyridine in 400Ml THF was added over a period of 60 minutes.

After the addition was completed, the mixture was warmed to roomtemperature and stirred overnight. The reaction mixture was poured intowater, extracted with ether, and washed with 5% NaHCO₃. The organiclayer was dried over MgSO₄, and the dry product was purified by columnchromatography using silica-gel and 1:1 hexane-CH₂ Cl₂ as the eluant,affording 98 mg (i.e., 98% yield) of a purple solid, mp 74°-5° C. IR(KBr pellet): (1736.5, 1721, 1609.1, 1265.7, 1231, 1196.2, 1089.5, 1090,686.9) cm⁻¹. NMR (CDCl₃): 7.27 ppm (d, 4.98 Hz, 2H), 7.02 ppm (d, 4.98Hz, 2H), 4.38 ppm (q, 6.64 Hz, 4H), 1.36 (t, 6.64, 6H). UV-VIS(nitrobenzene): 500 nm. Composition: 57% C, 4.2% H calculated; 57.36% C,4.31% H observed. This synthesis is schematically shown in FIG. 29.

EXAMPLE 11 Cyclopenta 2,1-b;3,4-b'!dithiophen-4-(bis carboxyheptyl)methylidene (BCHCPD)

In a 100 Ml round bottom flask, 1 g (9.6 mmol) of malonic acid, 2.23 g(19.2 mmol) of 1-heptanol, 0.1 g of p-toluenesulfonic acid and 60 Ml oftoluene were placed. The mixture was refluxed overnight under aDean-Stark head. The mixture was then washed with water, 5% NaHCO₃, andwater, dried over MgSO₄ and evaporated under vacuum, affording 2.50 g(83% yield) of the diester. IR (Neat): (2955, 2928, 2859, 1740.3,1755.8, 1466.4, 1331.3, 1269.6, 1180.8, 1149.9, 1011)cm⁻¹. NMR (CDCl₃):4.15 ppm (t, 6.7 Hz, 4H), 3.37 ppm (s, 2H), 1.66 ppm (m, 4H), 1.31 ppm(m, 16H), 0.90 ppm (m, 6H).

In a 50 ml round bottom flask, 5 ml of dry THF were chilled 0° C. undera nitrogen atmosphere. Then a solution of 650 Ml TiCl₄ in 1250 Ml Ccl₄was added dropwise with vigorous stirring. A bright yellow precipitatewas formed, and then a solution of 50 mg (0.26 mmol) of the ketone (IX),and 79 mg (0.26 mol) of diheptyl malonate in 5 Ml THF was added. Whenthe mixing was complete, a solution of 1080 Ml pyridine in 1000 Ml THFwas added over a period of 60 minutes. After the addition was completed,the mixture was warmed to room temperature and stirred overnight.

The reaction mixture was poured into water, extracted with ether, andwashed with 5% NaHCO₃. The organic layer was dried over MgSO₄, and thedry product was purified by column chromatography using silica-gel andhexane-CH₂ Cl₂ (1:1) as the eluant, affording 112 mg (91% yield) of apurple solid, mp 53°-4° C. IR (Kbr pellet): (2921.1, 2851.7, 1728.8,1269.6, 1242.5, 1200.1) cm⁻¹. NMR (CDCl₃): 7.28 ppm (d, 4.98 Hz, 2H),6.99 ppm (d, 4.98 Hz, 2H), 4.29 ppm (t, 5.8 Hz, 4H), 1.69 ppm (m, 4H),1.27 ppm (br. s, 16H), 0.86 ppm (m, 6H). UV-VIS (nitrobenzene): 502 nm.Composition: 65.82% C, 7.17% H calculated; 65.85C, 7.07% H, observed.This synthesis is schematically shown in FIG. 30.

EXAMPLE 12 Cyclopenta 2,1-b;3,4-b'!dithiophen-4-(bis carboxyhexadecyl)methylidene (BCHDCPD)

In a 100 Ml round bottom flask, 2 g (9.6 mmol) of malonic acid, 4.64 g(19.2 mmol) of 1-hexadecanol, 0.1 g of p-toluenesulfonic acid and 50 Mlof toluene were placed. The mixture was refluxed overnight under aDean-Stark head. The mixture was then washed with water, 5% NaHCO₃, andwater, dried over MgSO₄, and evaporated under vacuum, affording 4.24 g(80% yield) of the diester. IT (Kbr pellet): (2996, 2921, 2851, 1751.9,1717.2, 1474, 1466, 1400, 1362, 1184, 1045, 1018.7, 721.6) cm⁻¹.

In a 50 ml round bottom flask, 5 ml of dry THF were chilled to 0° C.under a nitrogen atmosphere. Then a solution of 650 Ml TiCl₄ in 1250 MlCcl₄ was added dropwise with vigorous stirring. A bright yellowprecipitate was formed, and then a solution of 50 mg (0.26 mmol) of theketone (IX), and 143.5 mg (0.26 mol) of dihexadecyl malonate in 5 Ml THFwas added. When the mixing was complete, a solution of 1080 Ml pyridinein 1000 Ml THF was added over a period of 60 minutes.

After the addition was completed, the mixture was warmed to roomtemperature and stirred overnight. The reaction mixture was poured intowater, extracted with ether, and washed with 5% NaHCO₃. The organiclayer was dried over MgSO₄, and the dry product was purified by columnchromatography using silica-gel and hexane-CH₂ Cl₂ as the eluant,affording 100 mg (50% yield) of a purple solid mp 64°-65° C. IR (KBrpellet): (2955.9, 2917.3, 2851.7, 1728.8, 1613, 1466.4, 1277.3, 1246.4,1207.8, 725.5, 676.3) cm⁻¹. NMR (CDCl₃): 7.27 ppm (d, 4.99 Hz, 2H), 7.00ppm (d, 4.98 Hz, 2H); 4.3 ppm (m, 4H), 1.69 ppm (m, 4H), 1.26 (m, 52H),0.88 (m, 6H). UV-VIS (nitrobenzene): 495 nm. Composition: 72.72% C,9.64% H calculated; 72.68% C, 9.78% H observed. This synthesis isschematically shown in FIG. 31.

Citations in the following list are incorporated by reference herein forthe reasons cited.

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Of course other substituents, particularly those known in the art tohave electron-withdrawing effects may be substituted for those specifiedin many of the following claims. Such substituents for W and/or Z areviewed as equivalents.

We claim:
 1. A polymer having a bandgap of less than about 1 eV and thestructure: ##STR10## where W and Z are CO₂ R; R is C₂ H₅, C₇ H₁₅, or C₁₆H₃₃ ; and n is 5 to
 500. 2. A polymer having a bandgap of less thanabout 1 eV and the structure: ##STR11## where W and Z are CO₂ R, R isC_(m) H_(2m+1), m is 1 to 16, and n is 5 to about 500.